1. Field of the Invention
The present invention relates to the field of fuel injectors.
2. Prior Art
Preferred embodiments of the present invention are directed toward fuel injectors for diesel engines, though the invention is not so limited. The performance of an engine such as a diesel engine, particularly with respect to emissions, is highly dependent on the performance of the fuel injector used. In general, the better atomization of the fuel by the injector nozzle, the lower the emissions will be, both in hydrocarbons and nitrous oxides. For this purpose, smaller injection orifices together with higher injection pressures through intensification are desired. However, it is still desired for the injector needle to rapidly close at the end of injection, as a slow closure as the intensification pressure drops will allow some injection with poor or no atomization, grossly increasing the hydrocarbon emissions. Consequently, techniques for direct needle control have recently been developed wherein closure of the needle is augmented by a fluid under pressure controllably acting on the needle to force the needle closed against substantial fuel pressures, thereby closing the needle before the fuel pressure drops sufficiently for a needle return spring to be able to close the needle.
Injection pressures as high as 3000 bar and even higher are now being considered. To rapidly close the needle at the end of injection at such pressures, a substantial force must be exerted on the needle. While the total needle motion may only be on the order of 0.010 inches, such a force causes the needle to close with a significant impact, which has been found to cause premature injector failure by the breaking off of the nozzle's tip, which in turn can lead to other damage of an engine. Accordingly, it is particularly important that rapid needle closure be achieved in injectors using high pressure injection without degradation of the nozzle, or at least without sufficient degradation of the nozzle during the useful life of the injector so as to provide any substantial likelihood of a nozzle tip breakage during that useful life.